Here's where things start to break down. People don't look for meetups in their apps - they look for meetups online. No one looks for a "SF singles app." They don't even go to the appstore for that - they go to Google. And despite the fact that I pulled this term out of a hat, guess who's first in Google for "SF singles meetup"? Meetup.com.
The second reason this doesn't apply - meetup isn't selling a SF singles app like a company sells a game. They're selling a platform to help people organize. By putting the app name in front, they put the product in back.
Honestly I think the fragmentation of apps would be a mess, and that it would ultimately result in lower visibility, awareness, and traffic figures for meetup.com as the meetups themselves become the brand.
You cannoy simply assume that a branding strategy/architecture that worked in one case will work as well for a different product or industry. Sometimes umbrella/family branding is the way to go.